1. Field of the Invention
This invention relates generally to voltage dividers or potentiometers, and more particularly, to a potentiometer which not only has no moving parts in the usual sense of that expression but is actuable by mere touch, as by the fingertip of an operator. Still more particularly, the invention also relates to a device, a paper cutter or the like for example, having an element such as a backgage which may be moved and positioned by means of a potentiometer according to the invention.
2. The Prior Art
Mechanical potentiometers have long been known in which, typically, a conductive element or wiper is axially movable along the outer surface of a resistor, such as a coil of conductive wire of known resistance, in electrical contact therewith. An electric potential of constant magnitude is applied to the opposite ends of the resistor, and the wiper and one of the ends are connected in an electric circuit also containing one or more elements to be controlled or otherwise acted upon. The magnitude of the resistance interposed in the circuit by the conductor depends upon the axial position of the wiper relative to the ends of the conductor, whereby it is possible to vary the potential applied to other elements of the circuit by moving the wiper in either axial direction. Obviously, the magnitude of this potential may never be greater than that of the constant overall potential applied to the ends of the conductor.
U.S. Pat. No. 4,651,123, issued Mar. 17, 1987 to L. P. Zepp discloses a sandwich-type linear potentiometer in which a pair of elongate conductive strips are carried on a pair of nonconductive flexible plastic substrates in spaced relationship. In use an upper one of the substrates is engaged by a spring-loaded ball assembly which can be moved longitudinally relative to the strips to bring them into contact with each other, the resistance provided by the potentiometer varying according to the location of the point of contact.
In another technology, so-called membrane switches are also now well known and in recent years have been increasingly incorporated in the electric control panels of such devices as microwave ovens and calculators in place of the previously customary push-button keypads. Such a control panel presents a smooth outer surface bearing graphic indicia which represent the various values or functions assigned to the membrane switches disposed below the surface and out of sight. Merely pressing the surface with the fingertip at one of the indicia will activate the respective switch therebeneath. Like mechanical switches, membrane switches are normally in one of only two conditions, namely an "on" or activated condition and an "off" or inactivated condition. They are available from various sources, one source being SSI Electronics, Inc. of Grand Rapids, Mich.
U.S. Pat. No. 4,975,676, issued Dec. 4, 1990 to V. B. Greenhalgh, discloses a touch-controlled circuit apparatus for use in regulating ovens and the like, which provides such switches by means of a flexible glass membrane spaced above a rigid support layer, electrical circuitry being printed on the facing surfaces of the glass membrane and the support layer. In addition to the switches, this circuitry also provides a continuously variable linear potentiometer actuated by finger pressure. By moving the finger in either of two linear directions, the user may increase or decrease the setting of a clock, minute timer, cook time, or stop time.
U.S. Pat. No. 5,550,339, issued Aug. 27, 1996 to J. E. Haugh, also discloses a flexible cover spaced above a substrate, both carrying conductive films. In this instance, when pressure is applied to the cover at any point relative to a nonconductive zero-point, thereby bringing the films into electrical contact, it is said that "intent, direction and magnitude" are thereby indicated and that this information may be used to control tools such as automobiles, computers, appliances, toys, laboratory equipment "and other diverse machines and devices." However, no such tools or the circuitry to control them are specifically described or illustrated.